1. The Degradation Process is Too Slow and Inefficient.
Many raw materials commonly used to produce biogas today take too long to degrade, or do not degrade properly at all. Those raw materials are typically made out of complex structures that are difficult for bacteria to access, and also contain non-degradable substances, like lignin.
This structure leads to long retention times inside the digester, resulting in a slow and inefficient process. The most common solution to this problem is to pre-treat the raw materials. And there is a range of pre-treatment techniques to choose from - depending on your needs.
The main issue is that pre-treating the feedstock requires high investment costs AND high operational costs. With such expenses, you will want to make sure you chose the right pre-treatment option for your specific AD process. Carefully testing and evaluating those options is key.
2. The Presence of Nutrients and Toxic Substances Is Poorly Managed
The microorganisms involved in the AD process depend on a large number of nutrients to function properly. Those microorganisms are also sensitive to many substances that can be toxic and hinder their activity. In order to put microroganisms in best conditions, it is essential to understand whether the substrate contains enough nutrients - and to make sure it is toxin-free.
When nutrition is low, or toxins are present, you can mix different substrates to balance the nutrients and limit the toxic influence. Alternatively, you can add direct nutrient supplements or counteracting agents.
However, both of these solutions have downsides. Extensive research needs to be done to identify what is missing in your substrate in the first place, understand what supplements to use, and how to best mix different substrates together.
3. The Knowledge of the Microbiology Is Limited
Anaerobic digestion is a very complicated process, involving a large number of microorganisms working together to degrade complex materials in multiple steps.
We know very little about the different microorganisms involved, or how they interact with each other. For this reason, most digesters are typically operated as a “black box” – with little awareness of what is actually going on inside. Of course it is difficult to optimise a process that we do not fully understand.
By learning about AD microbiology, we can understand how microbial populations work and optimise the process significantly.
4. The Dynamics of the AD Process Are Complex
Any slight change in conditions can disturb the AD process. In order to avoid any disturbance, digesters are often operated far below their maximum capacity.
Again, tackling this problem requires us to truly understand the way the microorganisms operate and work together.
But how can we study these interactions? Today, specialised computer models for anaerobic digestion can describe and simulate many of the complex changes and connections between microorganisms during the process, giving us a better idea of what to expect.
However, even though much progress has been made, there are still many aspects of the AD process that are unknown to the researchers. A lot of work still remain to fully understand the dynamics of the process and improve the way we operate the plant.
Now that we have the main challenges in mind, let’s discuss two existing methodologies that can be used to overcome them: batch and continuous fermentation tests.